at first I didn't understand what was happenning with the xp orbs and enemies dying on their own, because there are no attack animations or vfx.
I played a bit but there isn't much to do. I tried colliding with the boss to see the rate of damage etc but only managed to lose 1 hp before he died. you want to change the immunity timer or something. fullscreen would probably be better than windowed, if you can't get in settings by the next time.
Moving platforms can push you into terrain.